CLINICAL ARTICLE J Neurosurg Spine 30:111–118, 2019 Change in the cross-sectional area of the thecal sac following balloon kyphoplasty for pathological vertebral compression fractures prior to spine stereotactic radiosurgery Eric Lis, MD,1 Ilya Laufer, MD,2 Ori Barzilai, MD,2 Yoshiya Yamada, MD,3 Sasan Karimi, MD,1 Lily McLaughlin, BS,2 George Krol, MD,1 and Mark H. Bilsky, MD2 1Department of Radiology, Neuroradiology Service; and Departments of 2Neurosurgery and 3Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York OBJECTIVE Percutaneous vertebral augmentation procedures such as vertebroplasty and kyphoplasty are often per- formed in cancer patients to relieve mechanical axial-load pain due to pathological collapse deformities. The collapsed vertebrae in these patients can be associated with varying degrees of spinal canal compromise that can be worsened by kyphoplasty. In this study the authors evaluated changes to the spinal canal, in particular the cross-sectional area of the thecal sac, following balloon kyphoplasty (BKP) prior to stereotactic radiosurgery (SRS). METHODS The authors retrospectively reviewed the records of all patients with symptomatic vertebral compression fractures caused by metastatic disease who underwent kyphoplasty prior to single-fraction SRS. The pre-BKP cross- sectional image, usually MRI, was compared to the post-BKP CT myelogram required for radiation treatment planning. The cross-sectional area of the thecal sac was calculated pre- and postkyphoplasty, and intraprocedural CT imaging was reviewed for epidural displacement of bone fragments, tumor, or polymethylmethacrylate (PMMA) extravasation. The postkyphoplasty imaging was also evaluated for evidence of fracture progression or fracture reduction. RESULTS Among 30 consecutive patients, 41 vertebral levels were treated with kyphoplasty, and 24% (10/41) of the augmented levels showed a decreased cross-sectional area of the thecal sac. All 10 of these vertebral levels had preex- isting epidural disease and destruction of the posterior vertebral body cortex. No bone fragments were displaced posteri- orly. Minor epidural PMMA extravasation occurred in 20% (8/41) of the augmented levels but was present in only 1 of the 10 vertebral segments that showed a decreased cross-sectional area of the thecal sac postkyphoplasty. CONCLUSIONS In patients with preexisting epidural disease and destruction of the posterior vertebral body cortex who are undergoing BKP for pathological fractures, there is an increased risk of further mass effect upon the thecal sac and the potential to alter the SRS treatment planning. https://thejns.org/doi/abs/10.3171/2018.6.SPINE18206 KEYWORDS kyphoplasty; spine metastasis; epidural disease; oncology HE majority of patients who die from cancer have ten occur as a consequence of metastatic disease to the skeletal metastases, most commonly to the spine, spine and are a source of significant morbidity, often re- with spine metastasis present in approximately sulting in mechanical instability described as axial-load 30%T of oncological patients.19 Pain symptoms related to or movement-related pain. Balloon kyphoplasty (BKP) is spine metastases are often multifactorial and may include a minimally invasive procedure that can stabilize a patho- tumor-associated biological pain, radiculopathy, and me- logical vertebral compression fracture, offering patients chanical instability.15 Vertebral compression fractures of- decreased pain, increased mobility, and an overall im- ABBREVIATIONS BKP = balloon kyphoplasty; ESCCS = epidural spinal cord compression scale; PMMA = polymethylmethacrylate; ROI = region of interest; SSRS = spine stereotactic radiosurgery; VAS = visual analog scale. SUBMITTED February 22, 2018. ACCEPTED June 13, 2018. INCLUDE WHEN CITING Published online October 19, 2018; DOI: 10.3171/2018.6.SPINE18206. ©AANS 2019, except where prohibited by US copyright law J Neurosurg Spine Volume 30 • January 2019 111 Unauthenticated | Downloaded 09/23/21 09:51 PM UTC Lis et al. proved quality of life.1,4,9,13 The Cancer Patient Fracture stitutional guidelines with the patient under general an- Evaluation (CAFE) provided class I evidence that percu- esthesia in the interventional radiology department on a taneous cement augmentation offers meaningful, durable GE Innova CT/angiography system with C-arm fluoros- palliation in this very complicated cancer population.4 copy and CT capabilities.10,21 All BKP procedures were Spine stereotactic radiosurgery (SSRS) can deliver an ab- performed with the Kyphon Express kit (Medtronic Spine) lative radiation dose to the tumor while sparing adjacent utilizing either a bilateral transpedicular or a parapedicu- critical structures, most importantly the spinal cord and lar approach and 10- or 15-mm inflatable bone tamps. In cauda equina. The procedure is becoming more common all patients, the bone tamps were placed in the anterior as there is increasing evidence that it provides durable two-thirds of the vertebral body. Biopsies were obtained tumor control, overcoming the resistance often encoun- in all patients. Intraprocedural CT scanning with the bone tered with conventional external beam radiation.3,11,14,15,17 tamps inflated and immediate postkyphoplasty CT scan- Treating the compression fracture prior to SSRS can fa- ning were performed. At a later date, all patients under- cilitate the radiotherapy by providing pain relief that eases went post-BKP CT myelography as part of the treatment transfer to the treatment table and improves tolerance in planning for SSRS. the immobilization frame. However, concerns have arisen regarding the effect of the procedure on the spinal canal Pre-BKP Analysis 6,8 in the setting of vertebral metastases. An axial image at the intended kyphoplasty level that Metastatic disease to the vertebrae often results in lytic best demonstrated the greatest degree of thecal sac and destruction, possibly compromising the integrity of the spinal canal compromise was selected. The cross-section- posterior vertebral cortex. Additionally, epidural disease, al area of the thecal sac on the selected axial image was with or without posterior vertebral cortex destruction, can determined by drawing a region of interest (ROI) around also occur and result in varying degrees of spinal canal the thecal sac on a GE-PACS workstation, which then au- compromise. During BKP, bone tamps are inflated in the tomatically calculated the cross-sectional area of the the- collapsed vertebral body to create a cavity for the poly- cal sac (Figs. 1B and 2A). The greatest percentage loss methylmethacrylate (PMMA) to fill. Inflation of the bone of vertebral body height was also calculated by obtaining tamps can result in the mechanical displacement of tumor measurements from sagittal images at the plane of maxi- and/or bone fragments into the spinal canal, potentially mum loss of vertebral body height. Prefracture vertebral worsening or causing mass effect upon the thecal sac and body height was determined by measuring the height of resulting in symptomatic spinal cord, cauda equina, or the unfractured component of the vertebral body; if the nerve root compression. Even without symptomatic pro- vertebral body was uniformly collapsed, the prefracture gression, high-grade spinal cord or cauda equina com- height was estimated by measuring the vertebral body pression is a contraindication to SSRS; thus, kyphoplasty heights of the adjacent unfractured levels.7,16 The ROIs and can reduce the ability to deliver a cytotoxic radiation dose 6,8 percentage vertebral body collapse were determined by a within spinal cord or cauda equina constraints. The cur- CAQ (certificate of added qualification) neuroradiologist rent study specifically examined the effects of BKP on the (E.L.) and confirmed by a second CAQ neuroradiologist cross-sectional area of the thecal sac in patients with spine (S.K.). metastases and pathological compression fractures to as- Pre-BKP imaging studies (MRI, CT) of the levels that sess the risk of neurological progression or increased spi- underwent BKP were also analyzed for the appearance of nal canal compromise prohibiting the delivery of SSRS. metastatic disease (i.e., lytic, sclerotic, or mixed), integ- rity of the posterior vertebral body cortex, and presence of Methods epidural disease. Epidural disease at the level of the spinal Patients cord was characterized according to the epidural spinal cord compression scale (ESCCS),5 and epidural disease in Institutional review board approval was obtained for the lumbar spine below the conus medullaris was charac- this study. We retrospectively reviewed the records of all terized as causing mild to moderate central spinal canal patients with spine metastasis and symptomatic pathologi- compromise. cal vertebral compression fractures who had been referred for BKP for pain palliation prior to undergoing SSRS. All Intraprocedural Analysis patients had been evaluated by a multidisciplinary spine team consisting of neuroradiologists (E.L., G.K.), neuro- The intraprocedural fluoroscopic and CT images were surgeons (M.H.B., I.L.), and a radiation therapist (Y.Y.). reviewed to assess the underlying metastatic disease as None of the patients had mechanical radiculopathy, my- lytic, sclerotic, or mixed lytic-sclerotic in the patients who elopathy, or high-grade spinal cord or cauda equina com- did not have a preprocedural CT scan. Also, the integrity pression, and all were deemed acceptable candidates for of the posterior vertebral